Re: [PATCH RFC 05/18] accel/qda: Create compute CB devices on QDA compute bus

[Dmitry Baryshkov <dmitry.baryshkov@oss.qualcomm.com>]

On Tue, Feb 24, 2026 at 12:38:59AM +0530, Ekansh Gupta wrote:
> Add support for creating compute context-bank (CB) devices under
> the QDA compute bus based on child nodes of the FastRPC RPMsg
> device tree node. Each DT child with compatible
> "qcom,fastrpc-compute-cb" is turned into a QDA-owned struct
> device on qda_cb_bus_type.
> 
> A new qda_cb_dev structure and cb_devs list in qda_dev track these
> CB devices. qda_populate_child_devices() walks the DT children
> during QDA RPMsg probe, creates CB devices, configures their DMA
> and IOMMU settings using of_dma_configure(), and associates a SID
> from the "reg" property when present.
> 
> On RPMsg remove, qda_unpopulate_child_devices() tears down all CB
> devices, removing them from their IOMMU groups if present and
> unregistering the devices. This prepares the ground for using CB
> devices as IOMMU endpoints for DSP compute workloads in later
> patches.

Are we loosing the nsessions support?

> 
> Signed-off-by: Ekansh Gupta <ekansh.gupta@oss.qualcomm.com>
> ---
>  drivers/accel/qda/Makefile    |   1 +
>  drivers/accel/qda/qda_cb.c    | 150 ++++++++++++++++++++++++++++++++++++++++++
>  drivers/accel/qda/qda_cb.h    |  26 ++++++++
>  drivers/accel/qda/qda_drv.h   |   3 +
>  drivers/accel/qda/qda_rpmsg.c |  40 +++++++++++
>  5 files changed, 220 insertions(+)
> 
> diff --git a/drivers/accel/qda/Makefile b/drivers/accel/qda/Makefile
> index 242684ef1af7..4aded20b6bc2 100644
> --- a/drivers/accel/qda/Makefile
> +++ b/drivers/accel/qda/Makefile
> @@ -8,5 +8,6 @@ obj-$(CONFIG_DRM_ACCEL_QDA)	:= qda.o
>  qda-y := \
>  	qda_drv.o \
>  	qda_rpmsg.o \
> +	qda_cb.o \
>  
>  obj-$(CONFIG_DRM_ACCEL_QDA_COMPUTE_BUS) += qda_compute_bus.o
> diff --git a/drivers/accel/qda/qda_cb.c b/drivers/accel/qda/qda_cb.c
> new file mode 100644
> index 000000000000..77a2d8cae076
> --- /dev/null
> +++ b/drivers/accel/qda/qda_cb.c
> @@ -0,0 +1,150 @@
> +// SPDX-License-Identifier: GPL-2.0-only
> +// Copyright (c) Qualcomm Technologies, Inc. and/or its subsidiaries.
> +#include <linux/dma-mapping.h>
> +#include <linux/device.h>
> +#include <linux/of.h>
> +#include <linux/of_device.h>
> +#include <linux/iommu.h>
> +#include <linux/slab.h>
> +#include "qda_drv.h"
> +#include "qda_cb.h"
> +
> +static void qda_cb_dev_release(struct device *dev)
> +{
> +	kfree(dev);

Do you need to put the reference on the OF node?

> +}
> +
> +static int qda_configure_cb_iommu(struct device *cb_dev, struct device_node *cb_node)
> +{
> +	int ret;
> +
> +	qda_dbg(NULL, "Configuring DMA/IOMMU for CB device %s\n", dev_name(cb_dev));
> +
> +	/* Use of_dma_configure which handles both DMA and IOMMU configuration */
> +	ret = of_dma_configure(cb_dev, cb_node, true);
> +	if (ret) {
> +		qda_err(NULL, "of_dma_configure failed for %s: %d\n", dev_name(cb_dev), ret);
> +		return ret;
> +	}
> +
> +	qda_dbg(NULL, "DMA/IOMMU configured successfully for CB device %s\n", dev_name(cb_dev));
> +	return 0;
> +}
> +
> +static int qda_cb_setup_device(struct qda_dev *qdev, struct device *cb_dev)
> +{
> +	int rc;
> +	u32 sid, pa_bits = 32;
> +
> +	qda_dbg(qdev, "Setting up CB device %s\n", dev_name(cb_dev));
> +
> +	if (of_property_read_u32(cb_dev->of_node, "reg", &sid)) {
> +		qda_dbg(qdev, "No 'reg' property found, defaulting SID to 0\n");
> +		sid = 0;

Don't do the job of the schema validator. Are there nodes without reg?
No.

> +	}
> +
> +	rc = dma_set_mask(cb_dev, DMA_BIT_MASK(pa_bits));
> +	if (rc) {
> +		qda_err(qdev, "%d bit DMA enable failed: %d\n", pa_bits, rc);
> +		return rc;
> +	}
> +
> +	qda_dbg(qdev, "CB device setup complete - SID: %u, PA bits: %u\n", sid, pa_bits);
> +
> +	return 0;
> +}
> +
> +int qda_create_cb_device(struct qda_dev *qdev, struct device_node *cb_node)
> +{
> +	struct device *cb_dev;
> +	int ret;
> +	u32 sid = 0;
> +	struct qda_cb_dev *entry;
> +
> +	qda_dbg(qdev, "Creating CB device for node: %s\n", cb_node->name);
> +
> +	of_property_read_u32(cb_node, "reg", &sid);
> +
> +	cb_dev = kzalloc_obj(*cb_dev, GFP_KERNEL);
> +	if (!cb_dev)
> +		return -ENOMEM;
> +
> +	device_initialize(cb_dev);
> +	cb_dev->parent = qdev->dev;
> +	cb_dev->bus = &qda_cb_bus_type; /* Use our custom bus type for IOMMU handling */
> +	cb_dev->release = qda_cb_dev_release;
> +	dev_set_name(cb_dev, "qda-cb-%s-%u", qdev->dsp_name, sid);
> +
> +	qda_dbg(qdev, "Initialized CB device: %s\n", dev_name(cb_dev));
> +
> +	cb_dev->of_node = of_node_get(cb_node);
> +
> +	cb_dev->dma_mask = &cb_dev->coherent_dma_mask;
> +	cb_dev->coherent_dma_mask = DMA_BIT_MASK(32);
> +
> +	dev_set_drvdata(cb_dev->parent, qdev);
> +
> +	ret = device_add(cb_dev);
> +	if (ret) {
> +		qda_err(qdev, "Failed to add CB device for SID %u: %d\n", sid, ret);
> +		goto cleanup_device_init;
> +	}
> +
> +	qda_dbg(qdev, "CB device added to system\n");
> +
> +	ret = qda_configure_cb_iommu(cb_dev, cb_node);
> +	if (ret) {
> +		qda_err(qdev, "IOMMU configuration failed: %d\n", ret);
> +		goto cleanup_device_add;
> +	}
> +
> +	ret = qda_cb_setup_device(qdev, cb_dev);
> +	if (ret) {
> +		qda_err(qdev, "CB device setup failed: %d\n", ret);
> +		goto cleanup_device_add;
> +	}
> +
> +	entry = kzalloc(sizeof(*entry), GFP_KERNEL);
> +	if (!entry) {
> +		ret = -ENOMEM;
> +		goto cleanup_device_add;
> +	}
> +
> +	entry->dev = cb_dev;
> +	list_add_tail(&entry->node, &qdev->cb_devs);
> +
> +	qda_dbg(qdev, "Successfully created CB device for SID %u\n", sid);
> +	return 0;
> +
> +cleanup_device_add:
> +	device_del(cb_dev);
> +cleanup_device_init:
> +	of_node_put(cb_dev->of_node);
> +	put_device(cb_dev);
> +	return ret;
> +}
> +
> +void qda_destroy_cb_device(struct device *cb_dev)
> +{
> +	struct iommu_group *group;
> +
> +	if (!cb_dev) {
> +		qda_dbg(NULL, "NULL CB device passed to destroy\n");
> +		return;
> +	}
> +
> +	qda_dbg(NULL, "Destroying CB device %s\n", dev_name(cb_dev));
> +
> +	group = iommu_group_get(cb_dev);
> +	if (group) {
> +		qda_dbg(NULL, "Removing %s from IOMMU group\n", dev_name(cb_dev));
> +		iommu_group_remove_device(cb_dev);
> +		iommu_group_put(group);
> +	}
> +
> +	of_node_put(cb_dev->of_node);
> +	cb_dev->of_node = NULL;
> +	device_unregister(cb_dev);
> +
> +	qda_dbg(NULL, "CB device %s destroyed\n", dev_name(cb_dev));
> +}
> diff --git a/drivers/accel/qda/qda_cb.h b/drivers/accel/qda/qda_cb.h
> new file mode 100644
> index 000000000000..a4ae9fef142e
> --- /dev/null
> +++ b/drivers/accel/qda/qda_cb.h
> @@ -0,0 +1,26 @@
> +/* SPDX-License-Identifier: GPL-2.0-only */
> +/*
> + * Copyright (c) Qualcomm Technologies, Inc. and/or its subsidiaries.
> + */
> +
> +#ifndef __QDA_CB_H__
> +#define __QDA_CB_H__
> +
> +#include <linux/device.h>
> +#include <linux/of.h>
> +#include <linux/list.h>
> +#include <linux/qda_compute_bus.h>
> +#include "qda_drv.h"
> +
> +struct qda_cb_dev {
> +	struct list_head node;
> +	struct device *dev;
> +};
> +
> +/*
> + * Compute bus (CB) device management
> + */
> +int qda_create_cb_device(struct qda_dev *qdev, struct device_node *cb_node);
> +void qda_destroy_cb_device(struct device *cb_dev);
> +
> +#endif /* __QDA_CB_H__ */
> diff --git a/drivers/accel/qda/qda_drv.h b/drivers/accel/qda/qda_drv.h
> index bec2d31ca1bb..eb732b7d8091 100644
> --- a/drivers/accel/qda/qda_drv.h
> +++ b/drivers/accel/qda/qda_drv.h
> @@ -7,6 +7,7 @@
>  #define __QDA_DRV_H__
>  
>  #include <linux/device.h>
> +#include <linux/list.h>
>  #include <linux/mutex.h>
>  #include <linux/rpmsg.h>
>  #include <linux/xarray.h>
> @@ -26,6 +27,8 @@ struct qda_dev {
>  	atomic_t removing;
>  	/* Name of the DSP (e.g., "cdsp", "adsp") */
>  	char dsp_name[16];
> +	/* Compute context-bank (CB) child devices */
> +	struct list_head cb_devs;
>  };
>  
>  /**
> diff --git a/drivers/accel/qda/qda_rpmsg.c b/drivers/accel/qda/qda_rpmsg.c
> index a8b24a99ca13..5a57384de6a2 100644
> --- a/drivers/accel/qda/qda_rpmsg.c
> +++ b/drivers/accel/qda/qda_rpmsg.c
> @@ -7,6 +7,7 @@
>  #include <linux/of_device.h>
>  #include "qda_drv.h"
>  #include "qda_rpmsg.h"
> +#include "qda_cb.h"
>  
>  static int qda_rpmsg_init(struct qda_dev *qdev)
>  {
> @@ -25,11 +26,42 @@ static struct qda_dev *alloc_and_init_qdev(struct rpmsg_device *rpdev)
>  
>  	qdev->dev = &rpdev->dev;
>  	qdev->rpdev = rpdev;
> +	INIT_LIST_HEAD(&qdev->cb_devs);
>  
>  	qda_dbg(qdev, "Allocated and initialized qda_dev\n");
>  	return qdev;
>  }
>  
> +static void qda_unpopulate_child_devices(struct qda_dev *qdev)
> +{
> +	struct qda_cb_dev *entry, *tmp;
> +
> +	list_for_each_entry_safe(entry, tmp, &qdev->cb_devs, node) {
> +		list_del(&entry->node);
> +		qda_destroy_cb_device(entry->dev);
> +		kfree(entry);

Why can't you embed struct device into a structure together with the
list_node (and possibly some other data?)?

> +	}
> +}
> +
> +static int qda_populate_child_devices(struct qda_dev *qdev, struct device_node *parent_node)
> +{
> +	struct device_node *child;
> +	int count = 0, success = 0;
> +
> +	for_each_child_of_node(parent_node, child) {
> +		if (of_device_is_compatible(child, "qcom,fastrpc-compute-cb")) {
> +			count++;
> +			if (qda_create_cb_device(qdev, child) == 0) {
> +				success++;
> +				qda_dbg(qdev, "Created CB device for node: %s\n", child->name);
> +			} else {
> +				qda_err(qdev, "Failed to create CB device for: %s\n", child->name);

Don't loose the error code. Instead please return it to the caller.

> +			}
> +		}
> +	}
> +	return success > 0 ? 0 : (count > 0 ? -ENODEV : 0);
> +}
> +
>  static int qda_rpmsg_cb(struct rpmsg_device *rpdev, void *data, int len, void *priv, u32 src)
>  {
>  	/* Dummy function for rpmsg driver */
> @@ -48,6 +80,7 @@ static void qda_rpmsg_remove(struct rpmsg_device *rpdev)
>  	qdev->rpdev = NULL;
>  	mutex_unlock(&qdev->lock);
>  
> +	qda_unpopulate_child_devices(qdev);
>  	qda_deinit_device(qdev);
>  
>  	qda_info(qdev, "RPMsg device removed\n");
> @@ -83,6 +116,13 @@ static int qda_rpmsg_probe(struct rpmsg_device *rpdev)
>  	if (ret)
>  		return ret;
>  
> +	ret = qda_populate_child_devices(qdev, rpdev->dev.of_node);
> +	if (ret) {
> +		qda_err(qdev, "Failed to populate child devices: %d\n", ret);
> +		qda_deinit_device(qdev);
> +		return ret;
> +	}
> +
>  	qda_info(qdev, "QDA RPMsg probe completed successfully for %s\n", qdev->dsp_name);
>  	return 0;
>  }
> 
> -- 
> 2.34.1
> 

-- 
With best wishes
Dmitry